GB2035230A

GB2035230A - Run-flat pneumatic tyre

Info

Publication number: GB2035230A
Application number: GB7939220A
Authority: GB
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1978-11-20
Filing date: 1979-11-13
Publication date: 1980-06-18
Also published as: AU515168B2; GB2035230B; DE2946579C2; JPS5568406A; DE2946579A1; US4265288A; JPS6141763B2; AU5263179A; CA1120839A

Abstract

A pneumatic safety tire with a pair of annular rubber reinforcements having crescent sectional shape and applied to a tire carcass at tire sidewalls, the rubber of the reinforcements having a JIS hardness of not less than 70, a tensile stress (Mod25) after an aging test of not less than 10 kg/cm2, and a repulsive elasticity by Dunlop tripsometer of not less than 65%.

Description

1 GB 2 035 230 A 1

SPECIFICATION

Pneumatic safety tire This invention relates to a pneumatic safety tire.

A pneumatic safety tire aims to ensure continuous safe running after puncture (to be referred to as "run-flat", hereinafter) until replacement or proper repair of the punctured tire can be carried out, by having a means built in the tire for bearing the wheel load acting on the tire instead of bearing the wheel load by the internal penumatic pressure of the tire, which internal pneumatic pressure is normally maintained in the inner hollow space of the tire at a predetermined level but is lost upon sudden occurrence of a puncture. By 10 "wheel load" is meant the total load applied to one third wheel from a vehicle on which the tire is mounted.

Various types of means for bearing the wheel load in case of tire puncture are known, for instance U.S.

Patent No. 3 954 131 teaches the use of rubber reinforcements of the tire sidewalls which provide run-flat ability without adversely affecting the normal tire performance prior to a puncture, especially not requiring any reduction of normal running speed.

In short, the aforesaid known means for bearing the wheel load upon occurrence of a puncture uses rubber reinforcements which are crescent-shaped in cross-section and made of an elastomer having a comparatively high elasticity and arranged mainly at the inner surface of tire sidewall portions so as to extend from the bead portions to the hump portions of the tire, the maximum thickness of each rubber reinforcement being less than 15%, preferably 3% to 9%, of the maximum tire section width under inflated 20 conditions. The rubber reinforcements impart extra rigidity to the tire sidewall portions for bearing the wheel load after tire puncture by the thus reinforced tire sidewalls instead of bearing the wheel load by the internal pneumatic pressure of the tire.

However, the aforesaid known safety tire has a shortcoming in that it is difficult to determine criteria for setting an upper limit of the distance over which the run-flat is allowed while ensuring reproduction of the 25 proper performance characteristics inherent to the tire, because the required distance to be covered by the run-flat is generally uncertain and the time when the puncture is recognized is also uncertain. Accordingly, there is a tendency to exceed the safe run-flat distance, leading to breakage of the tire, or undertaking dangerous tire change operations on a road due to the fear of such tire breakage.

To obviate the aforesaid shortcoming, the present inventors have carried out special studies on tire breakage caused by excessive run-flat.

Generally speaking, the main cause of tire breakage due to excessive runflat is heat, and it is important to find out how to reduce the heat. Tire breakage due to running after occurrence of a tire puncture proceeds in the following manner.

1 Fiexure:Heat 1 Deterio --- > 1 ot 1 ge:nera- j ration1 1 sidewalisi tion of rubberl Increased flexure Therefore, the suppression of heat generation and prevention of thermal deterioration are essential for achieving a substantial improvement in the run-flat ability of a tire.

The inventors therefore analyzed the run-flat abilityfrom various considerations, especially physical properties of rubber relating to the run-flat ability, such as (1) hardness of rubber which is sufficient for bearing the wheel load with comparatively thin rubber reinforcements for the tire sidewalls while improving the heat dissipation, in contrast to comparatively thick rubber reinforcements utilized in the prior art for strengthening the tire, (2) the tensile stress of rubber after an aging test, which tensile stress plays an important role in suppressing deterioration of the rubber or ensuring a high heat-resistance of the rubber, 50 and (3) the repulsive elasticity of the rubber which contributes to the suppression of heat generation in the rubber. As a result, the inventors have succeeded in effectively improving the durability of run-flat ability.

The present invention provides a pneumatic safety tire, comprising a pair of annular bead portions, a carcass extending across the two bead portions, an annular tread portion formed on the outer peripheral surface of the carcass, a pair of sidewalls each extending between a bead portion and the corresponding 55 edge of the tread portion, a pair of rubber reinforcing members applied to the sidewalls, and a tread reinforcing belt layer embedded in tread rubber forming the tread portion while surrounding the carcass, wherein the rubber reinforcing members each comprise an elastomer having a JIS hardness of not less than 70, a tensile stress (Mod25) of not less than 10 kg/CM2 after an aging test for 24 hours in an inert atmosphere at 1400C 1'C, and a repulsive elasticity as measured by a Dunlop tripsometer of not less than 65%.

In a preferred embodiment of the invention the tire is a radial tire and the tread rubber thereof comprises an elastomer having a repulsive elasticity as measured by a Dunlop tripsometer of not less than 40%.

The inventors noted that, with a safety tire the sidewalls of which are provided with the aforesaid rubber reinforcements, repeated deformations of the tread portion of the tire during the run-flat tend to cause gradual breakdown of the tread rubber, especially at the boundaries between the tread rubber and the edges 2 GB 2035230 A 2 of a belt layer embedded therein, mainly due to deterioration caused by heat generation by shearing forces and shearing strains and the ensuring heat accumulation at the edges of the belt layer. To solve this problem, the physical properties of the rubber material for the tread portion, particularly the repulsive elasticity of the rubber, were analyzed from the standpoint of the contribution of such physical properties to the suppression of heat generation. Consequently, the present invention has succeeded in preventing the gradual breakdown at the tread portion and further in effectively improving the durability of the run-flat ability. In addition, the inventors have found that folding the belt layer edges or the use of special caps at the edges of the belt layer in constructing the tread portion is very effective in preventing the breakdown of the tread rubber.

More particularly, in a folded construction of the belt layer, the belt layer is formed of one or more carcass jo side belts of a certain width and one or more tread side belts of a different width, and all the belts are overlaid one on the other with the center lines thereof aligned and those edge portions of the wider belt or belts which extend beyond the narrower belt or belts are folded around the edges of the narrower belt or belts onto the latter belt or belts. Preferably, all the belts consist of steel cords, or the belt or belts of one of the aforesaid two sides consist of KIEVI-AR (a trademark of Du Pont de Nemour and Company) cords. On the 15 other hand, in the capped construction of the belt layer, steel cord belts are overlaid with a wide belt or belts on the inside and a narrow belt or belts on the outside, and cloths made of organic fiber cords, such as nylon cords, are applied to each belt so as to cover at least the opposite edges of each belt.

With the present invention, a considerable improvement in the running durability after puncture of a safety tire is achieved by using improved sidewall-reinforcing rubber members forthe tire, which sidewallreinforcing rubber members are made by using a rubber composition comprising a blend of natural rubber NR and butadiene rubber BR as a main ingredient and suitable additives selected from carbon black, stearic acid, zinc white, oil, sulfur, and one or more vulcanization accelerators.

For reference, the running durability after puncture of two conventional safety tires of sizes 195160A 5 and 185170-14were measured by drum tests, which tires were provided with sidewall-reinforcing rubber 25 members made of comparatively soft rubber (with a JIS hardness of 55) free from any serious heat-generating problem and comprising a blend of natural rubber NR and butadiene rubber BR added with a small amount of styrene butadiene rubber SBR. The results were 14 km and 18 km, respectively. Here, the "running durability after puncture" was determined by the following test; namely, the tire being tested was pressed against a test drum at a predetermined load, i.e. 335 kg (equivalent to a wheel load of 450 kg) for the 30 tire size 195/60-15 and 275 kg (equivalent to a wheel load of 385 kg) for the tire size 185170-14, with the air inlet valve of the tire fully open, and the drum was run at a peripheral speed of 80 km/hour until the tire was broken, and the distance thus run before the tire breakage was determined as the running durability after puncture of thattire. The maximum thickness of the sidewall-reinforcing rubber member corresponded to 4.4% (one side only, 1,160 grams) of the maximum tire section width under fully inflated condition for the tire 35 size 195/60-15 and 4.1 %(one side only, 750 grams) of the maximum tire section width under fully inflated condition for the tire size 195/70-14. The same maximum thicknesses of the sidewall-reinforcing rubber members were used in different specimens to be referred to in the specification.

Test specimens 1 of the aforesaid two tire sizes were made by forming sidewall-reinforcing rubber members of the same thickness as those of the aforesaid conventional reference tires of a rubber of JIS 40 hardness of 75 having increased amounts of butadiene rubber BR and styrene-butadiene rubber SBR and a reduced amount of natural rubber NR. Drum tests on these test specimens 1 showed improved running durabilities after puncture, namely 50 km and 63 km for the tire sizes 195160-15 and 185170-14, respectively.

In addition, test specimens 2 of the aforesaid two tire sizes were made by forming sidewall-reinforcing rubber members odf the same thickness as those of the aforesaid conventional reference tires of a blend 45 rubber of JIS hardness of 77 containing a further increased amount of butadiene rubber BR but without styrene-butadiene rubber SBR. Drum tests on those test specimens 2 showed low running durabilities after puncture, namely 29 km and 36 km for the tire sizes 195160-15 and 185170- 14, respectively.

Table 1 shows the measured values of physical properties of the rubbers in the tires thus tested, together with a tabulation of the aforesaid running durabilities after puncture of the reference and test specimen tires. 50 A comparative study of the aforementioned test results on the conventional reference safety tires and similar test specimens indicate that, to improve the running durability after puncture, in addition to the provision of a required rigidity while ensuring good heat dissipation by using thin sidewall-reinforcing rubber members of a rubber of high hardness, it is also necessary to improve the heat resistance of the rubber for the sidewall-reinforcing rubber members, in particular improvements both in the tensile stress 55 after aging and in the repulsive elasticity contributing to the suppression of heat generation are necessary.

it 1 1 3 GB 2 035 230 A 3 TABLE 1

Tire tested Item Conven- Test Test 5 tional, specimen specimen reference 1 1 JIS hardness 55 75 77 Tensile before aging 6.0 15.0 19.

stress Mod25 after aging 3.5 13.0 8.0 (kg/cM2) retaining factor 58 87 42 Repulsive elasticity by Dunlop tripsometer 66 59 75 Running durability 195160-15 14 50 29 after puncture (km) 185/70-14 18 63 36 20 Various compositions of the rubberforthe sidewall-reinforcing rubber members were prepared and tested, while using the composition of the test specimen 2 as a reference, which reference composition consisted of 70 parts of natural rubber NR, 30 parts of butadiene rubber BR, 75 parts of carbon black FEF, 3 parts of stearic acid, 3 parts of zinc white, 8 parts of oil, 6 parts of sulfur, and 1.0 part of vulcanization 25 accelerator. In particular, the effects of increasing the amount of butadiene rubber BR were checked. Rubber specimens No. 1 to No. 5 were prepared as shown in Table 2, and similar tires to those of Table 1 were made while using the rubber specimens in the sidewall-reinforcing rubber members of the same thickness as those of the tires of Table 1. Drum tests were carried out on the tires using the rubber specimens No. 1 to No.

5 for checking the running ability after puncture thereof, and the results are also shown in Table 2. As can be 30 seen from Table 2, the running durability after puncture was greatly improved by using the rubber compositions of Table 2.

TABLE 2

Rubber specimens No. 1 2 3 4 5 JIS hardness hd 71 73 79 74 77 Tensile stress before aging 17,3 17.0 21.4 17.0 20.5 Mod25 after aging 10.5 12.0 15.2 16.5 16.3 40 (kg/cM2) retaining factor 61.0 70.6 71.0 97.0 79.5 Repulsive elasticity by Dunlop tripsometer 75 77 73 71 81 Running durability 195/60-15 90 166 263 310 322 after puncture (km) 185/70-14 ill - - 380 - 45 Based on the results of the aforesaid tests,the present invention requiresthe use of rubberforthe sidewall-reinforcing rubber members which has a JiS hardness of not less than 70, a tensile stress Mod25 Of not less than 10 kg /CM2, and a tripsometer type repulsive elasticity of not less than 65%. Here, "aging" means the aging test conditions of JIS K6301-4, subject to the modifications of using an inert atmosphere, preferably a nitrogen atmosphere, and keeping the test temperature at 1400C 10C, in view of the special characteristics of the sidewall-reinforcing rubber members.

As regards the composition of the rubber, the rubber specimens No. 1 and No. 2 use a blend rubber consisting of 50 parts of natural rubber NR and 50 parts of butadiene rubber BR, and the rubber specimen 55 No. 1 contains 75 parts of carbon black GP17 while the rubber specimen No. 2 contains 60 parts of carbon black FEF, and the contents of the other ingredients of the rubber specimens No. 1 and No. 2 are similar to those of the test specimen No. 2 of Table 1. The rubber specimens No. 3 to No. 5 contain larger amounts of butadiene rubber Br and the amounts of other additives are slightly modified.

The underlined test results in Table 2 show that no damage or breakage was found on the tire side portions 60 including the sidewall-reinforcing rubber members by inspection from the outside, but upon disassembling the tires tested breakdowns were found at boundaries between the tread rubber and the edges of belt layers.

To overcome the breakdowns at the tread portion, further tests were carried out by using tires of the size 195/60-15 having tread portions made of low-heat-generating tread rubbers A to D the characteristics of which are set out in Table 3 and sidewall-reinforcing rubber members made of the rubber specimens No. 1 65 4 TABLE 3

Designation of test case Physical properties of tread rubber rubber member Internal temperature CC) JIS hardness Hd 300% modulus (kg /CM2) repulsive elasticity by Dunlop tripsometer (%) rubber specimen of Table 2 max. thickness 3) (%) (one side) weight used (9) on belt (depth 10 mm) sidewallreinforcing rubber member Running durability drum test 1) after puncture (km) field test 2)

Notes:

A B, B2 c, C2 center edge hump (depth) 10 mm) No. 1 No.1 5.4 5.4 1,500 1,500 70 103 92 92 61 D 62 47 No.4 No. 1 No. 4 4.4 5.4 4.4 1,160 1,500 1,160 63 No.1 5.4 1,500 60 83 - 73 widest point 93 89 85 78 (depth 8 mm) 613 819 310 205 313 85 1) With a load of 335 kg and at a speed of 80 km/hour.

2) Air inlet valves of front wheel tires were left open, with a load of 450 kg and at a speed of 80 km/hour.

3) Percentage of maximum thickness of sidewallreinforcing rubber member is based on the maximum tire section width under inflated condition.

k, 1, 1,251 820 1,443 375 220 435 11 1, 4 CD =r CD Z C:

Cr Cr o CD Cc 0-2) C = 0-0 0 N =r CD Ln. =r CL CD CD (D (D 0 C: M o C) r_ 0 =r 0 CD 0 Wa) (D 0 CD 3 0 cr =wr 0 Q o pr m 0 < (D CD 0) cr (D 3 p 0-0 3 0 0 3 =r -C5 CD 0 0 0 (D 3 CD c) W N) 0 W M tO W m 4 GB 2 035 230 A 5 Referring to Table 3, when a tread rubber having a high repulsive elasticity of not less than 40% which indicates a low heat generation level is used, the heat generated in the sidewall-reinforcing rubber member during run-flat is effectively absorbed, so that the internal temperature of the sidewall-reinforcing rubber member can be kept low, for remarkably improving the running durability after puncture. More particularly by comparison of the test cases B2 and C2 using the sidewall-reinforcing rubber members of rubber specimen No. 4, it is apparent that the use of the tread rubber having a high repulsive elasticity can improve the running durability after puncture by 2.5 times or more.

As regards the belt layer for reinforcing the tread portion, the tire for the test case C2 of Table 3 consisted of steel cord cloths with a cut angle of 70', and the inner cloth had a width of 171 mm while the outer cloth had a width of 160 mm. The variation of the running durability after puncture with modifications of the structure of 10 the belt layer was checked by using the tire of the test case C2 of Table 3 as a control tire. The results were as follows.

1. When the cut angle was reduced to 65', the running durability after puncture (by drum test) was reduced to 456 km, as compared with 820 km for the control tire.

2. When the widths of the inner and outer cloths were reduced to 160 mm and 150 mm, respectively, 15 while keeping the cut angle at70', the running durability after puncture was slightly reduced to 810 km.

3. On the contrary, when the inner and outer belt cloths were widened to 180 mm and 170 mm respectively, the running durability after puncture was improved to 1,030 km.

4. When a belt layer identical with that of the control tire was covered by a nylon cord cloth (190 mm wide) and the opposite edges of the belt layer were capped by edge portions of the nylon cloth, so as to 20 produce a capped belt structure, the running durability after puncture was greatly improved to 1,270 km, or improved by about 50%.

5. When the widths of the inner and outer cloths of the belt layer were widened to 240 mm and 165 mm, respectively, and the opposite edges of the inner cloth were folded back so as to form a 170 mm wide belt of folded structure, the running durability after puncture was improved to 1, 135 km, which is a similar 25 improvement to that achieved with the capped belt structure.

6. When the same folded belt structure of the belt layer as that of the preceding paragraph 5 was formed while using a KEVI-AR cord cloth as the outer cloth, the running durability after puncture was improved to 1,790 km, or doubled as compared with that of the control tire.

As described in the foregoing, the run-flat characteristics of a pneumatic safety tire according to the 30 present invention are so improved that continuous driving after puncture can be ensured without adversely affecting the repairability of the tire, regardless of any delay in recognizing the tire puncture or under any unfavourable conditions normally expected in regular automobile driving. Accordingly, the need to carry out a dangerous tire change operation on a road carrying heavy traffic can be eliminated.

The sidewall-reinforcing rubber members to be used in the tire of the present invention are disposed on 35 the inner side of the tire sidewall, and more particularly are attached to the inner surface of an inner rubber layer if such an inner rubber is used, or disposed between the inner rubber layer and the carcass plies, or attached to the inner surface of the carcass plies, or disposed between the carcass plies. Each sidewall-reinforcing rubber member may suitably have a crescent-shaped cross-section, that is the thickness of the sidewall-reinforcing rubber member gradually increases froms its one end at the tire bead portion 40 until it reaches its maximum thickness, and then its thickness gradually decreases as it extends toward the tire hump or further to the tread center. Thus, each sidewall-reinforcing rubber member is of annular belt-shape extending continuously in the circumferential direction of the tire as an integral part joined with the tire rubber. The maximum thickness of the sidewall-reinforcing rubber member relates to its hardness and is determined so as to bear the wheel load by co-operating with the tire sidewalls, and is preferably 4% 45 to 9% of the maximum tire section width under the inflated condition of the tire.

Each sidewall-reinforcing rubber member may contain short fibers, threads, cloths or other reinforcing elements, provided that the aforesaid heat-generating and heat-resisting characteristics are not adversely affected thereby. Such reinforcing elements may be advantageous from the standpoint of reducing the tire weight by the corresponding reduction of the amount of rubber, which may also lead to a cost reduction, and 50 from the standpoint of ensuring various performance characteristics of a high-speed tire.

The present invention can be advantageously applied to passenger car tires, especially radial tires for passenger cars, and also to tires for working cars with a comparatively low wheel load.

Claims

1. A pneumatic safety tire, comprising a pair of annular bead portions, a carcass extending across the two bead portions, an annular tread portion formed on the outer peripheral surface of the carcass, a pair of sidewalls each extending between a bead portion and the corresponding edge of the tread portion, a pair of rubber reinforcing members applied to the sidewalls, and a tread reinforcing belt layer embedded in tread 60 rubber forming the tread portion while surrounding the carcass, wherein the rubber reinforcing members each comprise an elastomer having a JIS hardness of not less than 70, a tensile stress (Mod25) of not less than 10 kg /CM2 after an aging test for 24 hours in an inert atmosphere at 140'C VC, and a repulsive elasticity as measured by a Dunlop tripsometer of not less than 65%.

2. A pneumatic tire as claimed in Claim 1, which is a radial tire, and wherein the said tread rubber thereof 65 6 GB 2 035 230 A 6 comprises an elastomer having a repulsive elasticity as measured by a Dunlop tripsometer of not less than 40%.

3. A pneumatic tire as claimed in Claim 2, wherein the said tread reinforcing belt layer comprises at least two annular belts of different widths and wherein opposite edges of a wider one of the said belts are folded 5 back onto opposite edges of a narrower one of the belts.

4. A pneumatic tire as claimed in Claim 3, wherein the said belt to be folded comprises KIEVI-AR cords.

5. A pneumatic tire as claimed in Claim 2, wherein opposite edges of the said tread reinforcing belt layer are covered by caps comprising cloths of organic fiber cords.

6. A pneumatic tire as claimed in Claim 5, wherein each said cap comprises nylon cord cloth.

7. A pneumatic safety tire according to Claim 1, substantially as herein described and designated by 10 reference letter, A, B,, B2, Cl, C2 or D in the aforegoing Table 3.

z Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon Surrey, 1980. Published by the Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.

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